The Na, K pump is a most important enzyme whose function is the basis of a number of vital physiological functions. The structure of the pump is that of a tetramer composed of two heterodimers; the functional unit is probably and alphaalpha dimer. The reaction mechanism of the pump is ping-pong. Little is known about the way in which the monomers function; but there are a number of phenomena which have been explained in terms of monomer interaction. We propose to examine some of these phenomena and obtain evidence which will exclude or support interaction. We will study the steady-state kinetics of ATP hydrolysis by means of product inhibition studies, use of modified enzyme and use of ATP analogues. We will also examine some characteristics of the steady-state kinetics of Mg interaction and of vanadate inhibition. We intend to measure the characteristics of the ion exchanges carried out by preparations in which the pump has been altered by physical or by enzymatic means, in part to determine whether the Na-Na and K-K exchanges can occur in the absence of the overall Na-K exchange. We also intend to measure pump characteristics in minimally altered preparations and compare them to the characteristics of enzyme preparations resulting from detergent treatment.